Predicting the impacts of climate change on marine ecosystem structure and functioning in Doubtful Sound, Fiordland

Healthy marine ecosystems provide a broad range of services that improve the health and wellbeing of people globally. Yet, human activities and anthropogenic climate change threaten to disrupt the biological processes that underpin marine ecosystem health and functioning. In order to understand how marine ecosystems and the services they support might be impacted by climate change we must first understand how they are structured. The Fiordland Marine Area is a place of great intrinsic, commercial, and cultural value, with a physical environment that supports unique marine communities. While certain aspects of the Fiordland ecosystem have been studied, the potential impacts of climate change are not well understood. Ecosystem models are one of the best available tools with which to predict the potential impacts of climate change on marine ecosystems. To build them, we need a good understanding of the species that exist in the ecosystem, and how they interact with one another, for example through their trophic links. In chapter 2 of this thesis, I quantified the diets of common reef fish in Doubtful Sound, Fiordland, assessing diet diversity, feeding strategies, and trophic partitioning between species across the Fiord’s environmental gradients. I found that some trophic partitioning occurs along with plasticity in feeding, and variability in prey availability likely influence the distribution of species throughout Doubtful Sound. In chapter 3, I developed ecosystem models of Fiordland marine communities and explored their response to a range of climate change scenarios. I found that a number of valuable commercial (rock lobster) or charismatic (bottlenose dolphins) species stand to be climate ‘losers’, while other groups such as CCAs and sponges are predicted to be climate ‘winners’. Overall, this work suggests that the impacts of climate change are likely to alter the structure of Fiordland marine ecosystems and reduce the provisioning of key commercial resources for fisheries and tourism. Environmental monitoring, mitigation of climate effects and adaptive management strategies should be brought to the forefront in order to limit these negative impacts and ensure long-term ecosystem functioning and value.